Technique for determining a tuning frequency of an audio receiver

ABSTRACT

A technique for determining a tuning frequency of an audio receiver includes interrupting a received radio frequency (RF) signal at an input of the audio receiver. Next, a modulated audio signal is injected into the input of the audio receiver. Then, it is determined whether the demodulated audio signal is present at an output of the audio receiver. If not, the frequency of the modulated audio signal is changed until the demodulated audio signal is detected at the output of the audio receiver.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Ser. No.10/740,332, filed Dec. 18, 2003.

TECHNICAL FIELD

The present invention is generally directed to an audio receiver and,more specifically, determining a tuning frequency of an audio receiver.

BACKGROUND OF THE INVENTION

Various commercially available after-market devices have been designedto intercept radio frequency (RF) transmissions at an input of an RFreceiver and inject a different transmission signal into the RFreceiver. In general, these devices use existing RF receivers, e.g.frequency modulation (FM) receivers, to implement additional audiofunctions, e.g., mobile phones, satellite digital audio radio systems(SDARS) and compact disc (CD) players.

Many of these devices detect a local oscillator (LO) frequency of an FMreceiver to determine a current channel of the receiver (tuner). Ingeneral, such after-market devices have been inserted between thereceiver and its associated antenna.

These devices have typically relied on the presumption that FM receiversuse the same tuner design or the same intermediate frequencies. Suchdevices work relatively well with FM receivers that have sufficient LOleakage such that the intermediate frequencies can be detected. However,there are many FM receivers that suppress LO leakage and/or usedifferent tuner architectures and, in these situations, the currentlyavailable after-market devices do not function adequately. In receiversthat suppress LO leakage, an operator of the receiver has been requiredto tune to a fixed frequency of operation for the operation for theafter-market device. Unfortunately, this eliminates any ability for anadded device to interrupt the current receiver channel, unless a user ison that channel.

What is needed is a device that, when placed between a radio frequency(RF) receiver and its associated antenna, determines a current channelof the receiver.

SUMMARY OF THE INVENTION

One embodiment of the present invention is directed to a technique fordetermining a tuning frequency of an audio receiver. Initially, areceived radio frequency (RF) signal at an input of an audio receiver isinterrupted. Next, a modulated audio signal is injected into the inputof the audio receiver. Then, it is determined whether a demodulatedaudio signal that corresponds to the modulated audio signal is presentat the output of the audio receiver. If not, the frequency of themodulated audio signal is changed until the demodulated audio signal isdetected at the output of the audio receiver.

According to another embodiment of the present invention, the modulatedaudio signal may be initially injected at a last known channel of theaudio receiver. According to still another embodiment of the presentinvention, the modulated audio signal is one of a tone, a sequence oftones, a set of tones and a pseudo random noise (PRN). According to yetanother embodiment of the present invention, the received RF signals areinterrupted responsive to an audio source. In another embodiment of thepresent invention, the modulated audio signal is one of an amplitudemodulated (AM) signal and a frequency modulated (FM) signal.

According to various embodiments of the present invention, audio contentfrom an audio source is provided at the output of the audio receiverwhen the demodulated audio signal is present at the output of the audioreceiver, thus, indicating that the modulated audio signal is tuned tothe current channel of the audio receiver.

According to a different embodiment of the present invention, amodulated audio signal is superimposed on a received radio frequency(RF) signal at an input of an audio receiver. Next, it is determinedwhether a demodulated audio signal that corresponds to the modulatedaudio signal is present at the output of the audio receiver. If theaudio signal is not present at the output of the audio receiver, thefrequency of the modulated audio signal is changed.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is an electrical block diagram of an exemplary audio system andan audio subsystem for implementing the present invention;

FIG. 2 is a flow chart of an exemplary routine for implementing oneembodiment of the present invention; and

FIG. 3 is a flow chart of an exemplary routine for implementing anotherembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to one embodiment of the present invention, an audio subsystemis implemented that injects an audio signal between a radio frequencyreceiver and its associated antenna. When commanded, via for example anadditional audio source, the subsystem interrupts a received RF signaland injects an audio signal at the last known frequency, whichstatistically speeds up tuning, or may step through a sequence offrequencies. The subsystem then looks for the expected audio signal atthe output of the audio receiver, e.g., at the speakers of the audiosystem. If the expected audio signal is not present at the output of theaudio receiver, the system changes to the next frequency and repeatsuntil the correct frequency is found. The subsystem may use a microphone(or other device) to detect the audio signal at the output of the audioreceiver. It should be appreciated that the known audio signal may be atone, a sequence of tones, a set of tones, a pseudo random noise (PRN)or other detectable input.

According to another embodiment of the present invention, an audiosubsystem continually monitors and tracks a current radio frequency (RF)channel and superimposes an audio signal on top of received RF signals.In general, the superimposed audio signal is low in power, as comparedto the received RF signal currently on the channel, such that a listenerdoes not detect the intrusion but the audio signal is detectable at theoutput of the audio receiver. As with the above-described technique, aknown pseudo random noise (PRN) may be superimposed that is unnoticeableto a user, but detectable. For example, if the PRN sequence is longenough, the superimposed signal may readily be detectable. As with theabove technique, the subsystem may, in general, step through a series ofchannels until the audio signal is detected at the output of the audioreceiver.

With reference to FIG. 1, an exemplary audio system 100 includes aprocessor 102 that is coupled to a memory subsystem 104, a display 120,an AM/FM tuner 124 and a plurality of audio sources 130. The processor102 controls audio content provided to a listener, via a the speaker112, and may also supply various information to a user, via the display120 and/or the speaker 112. As used herein, the term processor mayinclude a general purpose processor, a microcontroller (i.e., anexecution unit with memory, etc., integrated within a single integratedcircuit), an application specific integrated circuit (ASIC), aprogrammable logic device (PLD) or a digital signal processor (DSP). Thememory subsystem 104 includes an application appropriate amount ofmemory (e.g., volatile and non-volatile memory), which provides storagefor various routines that are used to tune the tuner AM/FM 124 and mayalso provide a storage area for one or more speech recognitionapplications.

As is also shown in FIG. 1, an audio input device 118 (e.g., amicrophone) is coupled to a filter/amplifier module 116. Thefilter/amplifier module 116 filters and amplifies the voice inputprovided by a user through the audio input device 118. Thefilter/amplifier module 116 is also coupled to an analog-to-digital(A/D) converter 114, which digitizes the voice input from the user andsupplies the digitized voice to the processor 102 which may execute aspeech recognition application, which causes the voice input to becompared to system recognized commands. In general, the audio inputdevice 118, the filter/amplifier module 116 and the A/D converter 114form a voice input circuit 119.

The processor 102 may execute various routines in determining whetherthe voice input corresponds to a system recognized command and/or aspecific operator. The processor 102 may also cause an appropriate voiceoutput to be provided to the user through the speaker or audio outputdevice 112. The synthesized voice output is provided by the processor102 to a digital-to-analog (D/A) converter 108. The D/A converter 108 iscoupled to a filter/amplifier section 110, which amplifies and filtersthe analog voice output. The amplified and filtered voice output is thenprovided to audio output device 112 (e.g., a speaker). The processor 102is also coupled to a global position system (GPS) receiver 140, whichallows the system 100 to determine the location of the receiver 140 andits associated motor vehicle.

An audio subsystem 150 allows various after-market devices, e.g., mobilephones, satellite digital audio radio systems (SDARS) and compact disc(CD) players, to utilize the audio system 100 installed within a motorvehicle. As is shown, an antenna 125, associated with the motor vehicle,is coupled to a switch/coupler 151, whose output is coupled to an inputof the tuner 124. The switch/coupler 151 may be implemented as either aswitch or a coupler and, as discussed further below, the modulated audiooutput provided from a modulator 162 replaces the RF signal received bythe antenna 125 when the switch/coupler 151 is a switch. When theswitch/coupler 151 is a coupler, the modulated audio output providedfrom the modulator 162 is superimposed on the signal received via theantenna 125. It should be appreciated that, in either case, the signalprovided through the modulator 162 is only provided at the output of theaudio system 100 when the signal provided from the modulator 162 ismodulated at a frequency that corresponds to the current channel of thetuner 124.

The subsystem 150 also includes a processor 152 that is coupled to adetector 154, the modulator 162, a multiplexer 160, an audio signalgenerator 156 and an external audio source 158. When the switch/coupler151 is implemented as a switch, the processor 152 controls whether theoutput from the antenna 125 or the modulator 162 is provided to theinput of the tuner 124. When the switch/coupler 151 is implemented as acoupler, a separate control line is not required (from the processor 152to the coupler) as the signal provided by the modulator 162 issuperimposed on the RF signal received via the antenna 125.

As is shown in FIG. 1, the detector (e.g., a microphone) 154 is coupledto the processor 152 and provides an indication to the processor 152whether a signal provided via the modulator 162 is present at theoutput, i.e., at the speaker 112, of the audio system 100. If the signalis not detected via the detector 154, the processor 152 controls themodulator 162 to step to a next frequency or next channel. The processor152 controls the multiplexer 160 to provide either a signal from theaudio signal generator 156 or the external audio source 158. The signalfrom the audio signal generator 156 may take various forms, such as atone, a sequence of tones, a set of tones or a pseudo random noise(PRN), which is utilized by the processor 152 to determine whether themodulator 162 is tuned to an appropriate frequency.

When the detector 154 indicates that the signal provided by the audiosignal generator 156 is present at the output of the audio system 100,the processor 152 controls the multiplexer 160 to select an audio signalfrom the audio source 158. The output from the audio source 158 is thenmodulated by the modulator 162 before being provided to an input of thetuner 124, via the switch/coupler 151, and ultimately to a listener, viathe speaker 112.

As is discussed above, when the switch/coupler 151 is implemented as aswitch, the processor 152 causes the received radio frequency (RF)signal at the input of the audio receiver (i.e., the tuner 124) to beinterrupted and injects a modulated audio signal provided by the audiosignal generator 156 at the input of the audio receiver (tuner 124).Upon determining that a demodulated audio signal that corresponds to themodulated audio signal is not present at the output of the tuner 124,the processor 152 changes the frequency of the modulated audio signalprovided by the audio signal generator 156. According to one embodimentof the present invention, the modulated audio signal is initiallyprovided at a last known radio frequency channel.

With reference to FIG. 2, a routine 200 is illustrated, which isimplemented by the processor 152 in determining a tuning frequency ofthe tuner 124. Initially, in step 202, the routine 200 is initiated, atwhich point control transfers to step 204, where the processor 152causes the RF signal received via the antenna 125 to be interrupted bycontrolling the switch within the switch/coupler 151. Next, in step 206,the processor 152, by controlling the modulator 162, the multiplexer 160and the audio signal generator 156, causes an injected modulated audiosignal to be provided to an input of the tuner 124. Then, in decisionstep 208, the processor 152 determines whether a demodulated audiosignal that corresponds to the modulated audio signal is present at theoutput of the tuner 124, e.g., at the speaker 112.

As discussed above, the processor 152 determines whether the demodulatedaudio signal is present at the output of the tuner 124 by examining asignal received by the detector 154. When the processor 152 determinesthat the demodulated audio signal is present at the output of the tuner124, the processor 152 causes the multiplexer 160 to switch to provideaudio content from the audio source 158 in step 212. However, when thedemodulated audio signal is not present at the output of the tuner 124in step 208, the processor 152 causes the modulator 162 to changefrequency in step 210, at which point control is transferred to step206. In step 208, when the demodulated audio signal is present at theoutput of the tuner 124, control transfers to step 212 where audiocontent is provided from the audio source 158, before terminating theroutine 200 in step 214.

With reference to FIG. 3, according to another embodiment of the presentinvention, the processor 152 implements a routine 300, which isinitiated in step 302. Next, in step 304, the processor 152 controls themodulator 162 to cause a modulated audio signal (provided by the audiosignal generator 156 via the multiplexer 160) to be superimposed on theRF signal received via the antenna 125. Next, in decision step 306, theprocessor 152 determines whether a demodulated audio signal thatcorresponds to the modulated audio signal is present at the output ofthe tuner 124. As is discussed above, the processor 152 determineswhether the audio signal is present at the output of the tuner 124 byexamining an output signal provided by the detector 154.

In step 306, when the processor 152 does not detect the demodulatedaudio signal at the output of the audio system 100, control transfers tostep 308. In step 308, the processor 152 controls the modulator 162 tochange the modulation frequency, at which point control transfers tostep 304. In decision step 306, when the demodulated audio signal ispresent at the output of the tuner 124, control transfers to step 310and the processor 152 controls the multiplexer 160 to couple the outputfrom the audio source 158 to the modulator 162, which is then providedvia a coupler (associated with the switch/coupler 151) to the input ofthe tuner 124. Thus, the processor 152 controls the audio source 158,the multiplexer 160 and the modulator 162 to provide audio content fromthe audio source 158 at the output of the audio system 100 beforeterminating the routine 300 in step 312.

Accordingly, a number of techniques have been described herein thatallow an after-market audio source, installed within a motor vehicle, toutilize a radio frequency (RF) receiver installed in the motor vehicleto provide audio content from the audio source to an occupant of themotor vehicle.

The above description is considered that of the preferred embodimentsonly. Modifications of the invention will occur to those skilled in theart and to those who make or use the invention. Therefore, it isunderstood that the embodiments shown in the drawings and describedabove are merely for illustrative purposes and not intended to limit thescope of the invention, which is defined by the following claims asinterpreted according to the principles of patent law, including thedoctrine of equivalents.

1-7. (canceled)
 8. A method for determining a tuning frequency of anaudio receiver, comprising the steps of: superimposing a modulated audiosignal on a received radio frequency (RF) signal at an input of an audioreceiver; determining whether a demodulated audio signal thatcorresponds to the modulated audio signal is present at an output of theaudio receiver; and changing a frequency of the modulated audio signalwhen the demodulated audio signal is not present at the output of theaudio receiver.
 9. The method of claim 8, wherein the modulated audiosignal is initially provided at a last known channel of the audioreceiver.
 10. The method of claim 8, wherein the modulated audio signalis one of a tone, a sequence of tones, a set of tones and a pseudorandom noise (PRN).
 11. The method of claim 8, wherein the received RFsignals are interrupted responsive to an audio source.
 12. The method ofclaim 8, wherein the modulated audio signal is one of an amplitudemodulated (AM) signal and a frequency modulated (FM) signal.
 13. Themethod of claim 8, further comprising the step of: providing audiocontent from an audio source at the output of the audio receiver whenthe demodulated audio signal is present at the output of the audioreceiver.
 14. The method of claim 13, wherein the audio source is one ofa mobile telephone, a satellite digital audio receiver (SDAR) system anda compact disk (CD) player. 15.-18. (canceled)
 19. An audio subsystem,comprising: an audio signal generator for providing an audio signal; adetector for detecting a demodulated audio signal provided at an outputof an audio receiver; a modulator coupled to the audio signal generator,the modulator providing a modulated audio signal that corresponds to theaudio signal provided by the audio signal generator; and a processorcoupled to the audio signal generator, the detector and the modulator,wherein the processor is configured to execute code for causing theprocessor to perform the steps of: superimposing the modulated audiosignal on a received radio frequency (RF) signal at an input of theaudio receiver; determining whether the demodulated audio signal ispresent at the output of the audio receiver, wherein the demodulatedaudio signal corresponds to the modulated audio signal; and changing afrequency of the modulated audio signal when the demodulated audiosignal is not present at the output of the audio receiver.
 20. Thesubsystem of claim 19, wherein the modulated audio signal is initiallyprovided at a last known channel of the audio receiver.
 21. Thesubsystem of claim 19, wherein the audio signal provided by the audiosignal generator is one of a tone, a sequence of tones, a set of tonesand a pseudo random noise (PRN).
 22. The subsystem of claim 19, whereinthe processor is configured to execute additional code that causes theprocessor to perform the addition step of: providing audio content froman audio source at the output of the audio receiver when the demodulatedaudio signal is present at the output of the audio receiver.
 23. Amethod of employing an audio subsystem for determining a tuningfrequency of an audio receiver, wherein the audio subsystem comprises anaudio signal generator for providing an audio signal, a detector fordetecting a demodulated audio signal provided at an output of the audioreceiver, a modulator coupled to the audio signal generator, themodulator providing a modulated audio signal that corresponds to theaudio signal provided by the audio signal generator, and a processorcoupled to the audio signal generator, the detector and the modulator,said method comprising the steps of: superimposing a modulated audiosignal on a received radio frequency (RF) signal at an input of an audioreceiver; determining whether a demodulated audio signal thatcorresponds to the modulated audio signal is present at an output of theaudio receiver; and changing a frequency of the modulated audio signalwhen the demodulated audio signal is not present at the output of theaudio receiver.